Typical ratchet mechanisms for wrenches and the like include a housing having a cylindrical bore defining inwardly facing ratchet teeth on the cylindrical surface of the bore, a work-turning member received for rotation within the bore and a rectangular shank on the work-turning member extending outwardly from one side of the housing to engage a socket or the like.
The work-turning member generally carries a pawl within the cylindrical bore and has pawl teeth extending outwardly at appropriate locations on the pawl to enable engagement of the pawl teeth with the ratchet teeth of the housing. A mechanism is provided to move the pawl in order to cause rotation of the work-turning member with the housing in one rotational direction only, the direction of engagement being selectable by the operator.
In many prior reversible ratchet mechanisms, the pawl has been mounted on a pivot shaft, as shown, for example, in U.S. Pat. Nos. 3,393,587; 3,467,231 and 3,532,013. In such mechanisms, the strength of the ratchet wrench depends upon both the strength of the pawl and the strength of the pivot shaft. In order to increase the strength of the pivot shaft, a relatively large bore must be made through the pawl, thereby weakening the strength of the pawl itself. Such ratchet mechanisms are also relatively expensive to make, since the pawl must be provided with two sets of teeth, the pivot shaft must be firmly fixed to the work-turning member, and the work-turning member must be bored and machined to provide a spring mechanism to rotate the pawl about the pivot shaft.
In order to increase the strength of ratchet mechanisms, other prior wrenches have utilized a shifting pawl rather than a rotating pawl. Examples of such mechanisms are shown in U.S. Pat. Nos. 3,369,416; 3,393,780; 3,436,992; 3,306,940 and 3,783,703. In many of these ratchet mechanisms, openings in the pawl itself are minimized or eliminated. Forces exerted by the ratchet housing on the pawl can be compression forces on the pawl, rather than forces transmitted to a pivot shaft. In U.S. Pat. No. 3,306,940, the ratchet action of the pawl is reversed by shifting a coil spring which extends axially down into a large bore in the pawl. This bore weakens the pawl. The spring is caused to move by a shifting plate which is movable above the work-turning member and which is engaged with the work-turning member on the opposite side thereof from the pawl. In U.S. Pat. No. 3,783,703, the pawl is shifted by a wire spring which extends across the top of the work-turning member. At the pawl, the wire spring is inserted into a small bore in the pawl. The spring extends on both sides of a central screw which enters the work-turning member, and also engages a pin extending downwardly from a cap member which, when it is rotated, shifts the end of the spring opposite the pawl and thereby carries the pawl to a new position in response to tension placed on the spring. In practice, the ratchet mechanism shown in the '703 patent is constructed with a rectangular shaped wire spring rather than the heart shaped spring shown in the patent. The corners of the rectangular wire spring are flexed during operation and are subject to failure after repeated use. Also, two chordal recesses must be cut in the work-turning member, one for the pawl and another to permit the spring operating pin to extend vertically downwardly from the cap.
In both U.S. Pat. No. 3,606,940 and No. 3,783,703, almost the entire area above the work-turning member is required for the sweeping motion of either the plate or the wire spring which operates the pawl. In both mechanisms, a central screw holds the operating member to the work-turning member. Recesses, one for the pawl and one for the parts of the operating mechanism, must be cut on opposite sides of the central screw. The area of the work-turning member opposite the pawl is not available for other uses, such as a second pawl, and the unused area at the center of the work-turning member is not large enough to receive a quick-release mechanism.
Examples of quick-release mechanisms are shown in U.S. Pat. Nos. 3,393,587 and 3,532,013. Prior to the introduction of such mechanisms, a spring ball detent was typically provided on the shank of the work-turning member to retain a socket or the like. Removal of the socket from the shank was accomplished by manual pressure overcoming the spring of the ball detent. Quick-release mechanisms utilize a shaft extending through the work-turning member and including a beveled recess which operates the ball. The shaft of the quick-release mechanism is spring loaded into the shank in a manner such that the ball is urged out of the shank to retain the socket. When it is desired to release the socket, the protrusion of the shank through the opposite side of the work turning member is depressed, allowing the ball to move freely into the shank and the socket to move freely off the shank. As will be seen from an examination of the patents noted, a quick-release mechanism requires a significant amount of space at the center of the work-turning member, space which has not previously been available in shifting pawl ratchet mechanisms of the type shown in U.S. Pat. Nos. 3,606,940 and 3,783,703, in which the pawl shifts along a chordal recess in the work-turning member.